how can I pass an equation as input parameter to function

I write s function which take two parameter the first is an equation and the second is an integer number and I want to substitute with this number in the equation and return the result.

function result=sub(a,c)
%UNTITLED3 Summary of this function goes here
%   Detailed explanation goes here
result=subs(a,c);

end

when I test it on command window I write

     >> result=sub(2*x,1)

I get an error

??? Undefined function or variable 'x'.

Answer 1

[Eman Ahmed Elsayed]

I solved my problem

I wrote the function like the following

>> f=@(x) 2*x + 1

and then passed it to the function

[Ayesha Khan]

thanks